<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./jquery-3.1.1.js"></script>
</head>
<body>
    <input type="text" >
    点击其他地方，让我失去焦点
</body>
<script>
    $(function(){
        $('input').attr('placeholder','我是提示信息')
        $('input').blur(function(){
            // console.log(this)
            $(this).attr('placeholder','我是提示信息')
        })
        $('input').focus(function(){
            $(this).removeAttr('placeholder');
        })
    })
</script>
</html>